1. Technical Field of the Invention
The present invention relates to an exhaust structure in an engine for an automobile, the engine comprising a cylinder head which includes exhaust ports in its rear face, an engine block, and a crankshaft disposed in a lateral direction of a vehicle body; the exhaust structure comprising an exhaust manifold which is connected to the exhaust ports and which includes a collecting portion, and a substantially cylindrical exhaust emission control device which is disposed in the rear of the engine block and which includes a connection at its upper end; the collecting portion is connected to the connection.
2. Description of the Related Art
In a general automobile of a front-engine and front-drive type, an engine is laterally disposed so that a crankshaft extends along a lateral direction of a vehicle body. An intake manifold is connected to a rear face of a cylinder head, and an exhaust manifold is connected to a front face of the cylinder head. On the other hand, there is another type of automobile in which an intake manifold is connected to a front face of a cylinder head of a laterally-disposed engine, and an exhaust manifold is connected to a rear face of the cylinder head. In this type, a so-called straight-down-type exhaust emission control device is connected to a collecting portion of the exhaust manifold extending rearwards and downwards from the rear face of the cylinder head. The exhaust emission control device is formed into a substantially cylindrical shape, and the collecting portion of the exhaust manifold is conventionally connected to a connection formed at a central portion of an upper face of the exhaust emission control device.
Immediately after starting of the engine, the exhaust emission control device is in an inactive state and for this reason, it is necessary to heat the exhaust emission control device by heat of an exhaust gas to early activate the exhaust emission control device. For this purpose, it is desirable that travel wind is prevented as much as possible from acting on the exhaust manifold to maintain the temperature of the exhaust gas flowing into the exhaust emission control device at a high level. However, the diameter of the exhaust emission control device is considerably large, and if the exhaust manifold is connected to the connection formed at the central portion of the upper face of the exhaust emission control device, the exhaust manifold is parted from the rear face of the engine block, and travel wind is thus liable to act on the exhaust manifold. As a result, there is a possibility that the early activation of the exhaust emission control device is impeded.
In addition, it is desirable that a collision stroke permitting the retraction of the engine upon the frontal collision of the automobile is set as large as possible. However, if the exhaust manifold leading to the exhaust emission control device is parted rearwards from the rear face of the engine block, the following problem is encountered: the exhaust manifold having a high rigidity interferes with other members such as a steering gear box and the like, resulting in a reduction in the collision stroke.
The present invention has been accomplished with the above circumstance in view, and it is an object of the present invention to ensure that, in a rear-wall-discharging-type engine including a straight-down-type exhaust emission control device, an exhaust manifold connecting exhaust ports to the exhaust emission control device is located as close as possible to a rear face of an engine block.
To achieve the above object, according to a first feature of the present invention, there is provided an exhaust structure in an engine for an automobile, the engine comprising a cylinder head which includes exhaust ports in its rear face; an engine block; and a crankshaft disposed in a lateral direction of a vehicle body. The exhaust structure comprises an exhaust manifold which is connected to the exhaust ports and which includes a collecting portion; and a substantially cylindrical exhaust emission control device which is disposed in the rear of the engine block and which includes a connection at its upper end. The collecting portion is connected to the connection. The position of the connection of the exhaust emission control device is eccentric toward the engine block with respect to an axis of the exhaust emission control device.
With the above arrangement, the position of the connection of the exhaust emission control device is eccentric toward the engine block with respect to the axis of the exhaust emission control device. Therefore, the exhaust manifold can be disposed as close as possible to the rear face of the engine block, and thus it is possible to prevent travel wind from colliding with the exhaust manifold during cold operation of the engine immediately after starting of the engine to prevent a drop in temperature of an exhaust gas, thereby enabling the early raising of the temperature of the exhaust emission control device to inhibit the discharging of an emission. Moreover, since the exhaust manifold is disposed near the rear face of the engine block, it is possible to expand the collision stroke permitting the retraction of the engine upon the frontal collision to absorb a shock.
According to a second feature of the present invention, in addition to the arrangement of the first feature, there is provided an exhaust structure in an engine for an automobile in which the collecting portion of the exhaust manifold has a shape elongated in a direction of the crankshaft.
With the above arrangement, the collecting portion of the exhaust manifold has the shape elongated in the direction of the crankshaft. Therefore, all exhaust pipes constituting the exhaust manifold can be located still closer to the engine block in the vicinity of the collecting portion, thereby further enhancing an effect of early raising the temperature of the exhaust emission control device and an effect of expanding the collision stroke.